HomeMy WebLinkAboutPA2021-305_20211221_Floor Elevation Memo_08-17-2021Geotechnical C Geologic C Coastal C Environmental
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M E M O R A N D U M
DATE: August 17, 2021
TO:Brandon Architects
FROM: David Skelly, PE
SUBJECT:Finished Floor Elevation Newport Bay and Ocean Properties.
Currently the maximum historical water elevation in Newport Bay is about elevation 7.7 feet
NAVD88. On the open coast, it is higher, closer to elevation 8.5 feet NAVD88. Also on
the open coast shoreline wave runup can reach elevation +15 feet NAVD88. Currently
sea level is rising, however, there is little agreement on the rate of rise over the coming
decades. With sea level rise (SLR) these extreme water elevations will only go
proportionally higher. The regulatory agencies now require that the design of new
residential structures account for up to 6 feet of SLR over the next 75 years. The current
minimum finished floor (FF) elevation in many areas of Newport Bay is +9 feet NAVD88.
This is problematic in light of SLR because as little as 1.3 feet (9 feet -7.7 feet) of SLR can
result in flooding of residences in the Newport Beach ocean and bay area.
Many properties (the majority) in the bay area have bulkheads, which can be increased in
height as sea level rises to keep this flooding from occurring. However, there are areas
where there are no bulkheads like on Bay Island, Lido Island, and the Balboa Peninsula.
Bay and ocean waters can flow to homes and streets without being exclude by a bulkhead.
Some SLR models have 1.3 feet of SLR predicted in as soon as the year 2040, less than
2 decades from now. It is not clear that even small island communities, let alone larger
areas can be protected in this relatively short time frame (about 2 decades). With this
potential for flooding considered, new development should have a FF as high as
reasonably possible. In addition, the City is requiring the ability to add waterproofing to
new residences up to elevation +14.4 feet NAVD88. It is our recommendation that the
best way to flood proof development is to have the FF as high as reasonably possible.
As a quick aside, some new oceanfront properties on Seashore Drive are now required to
be above elevation +16 feet NAVD88, with FF around +17.5 feet NAVD88.
PA2021-305